Well, i don't know is it the correct or common procedure but i usually like to program all the ins units with different waypoints, for example in this aircraft, waypoints 1-9 to ins-1, waypoints 10-18 to ins 2 and waypoints 19-27 to ins 3. But in the Concorde, how can i switch between those 3 units? For example in the A300 for fsx, there was a "INS1-INS2" switch, i was using that switch to switch between ins units. 

You might find more assistance at the colimata forum at the org.